In a patent document 1, there describes a method for manufacturing a heat exchanger plate to exchange heat or the like while fluid is flowing through a channel formed in a base member. A lid groove opening to a surface of the base member and a concave groove formed on a bottom surface of the lid groove are formed in the base member. When a heat exchanger plate is manufactured, a lid plate is disposed in the lid groove, and a friction stir welding is performed to a butting portion of a side surface of the lid plate and a side wall of the lid groove. When the friction stir welding is performed, a stirring pin of a rotary tool is inserted into a deep position of the butting portion while a bottom surface of a shoulder of the rotary tool is in contact with the base member and the lid plate. Air-tightness and water-tightness of the heat exchanger plate can be improved by performing the friction stirring to the deep position of the butting portion.